Low dark count rate, high detection efficiency and accurate timing resolution are the three most desired features of a single-photon detector (Hadfield, 2009, Nat. Photon., 3(12): 696-705; Eisaman et al., 2011, Rev. Sci. Instrum., 82(7): 071101) These characteristics can be combined to one figure-of-merit for single-photon detectors, for example the noise equivalent power (NEP). Detectors with low noise performances are increasingly sought after for applications in both quantum and classical technology. In particular, linear optics quantum information processing crucially relies on the availability of low dark count rate single-photon detectors (Hadfield, 2009, Nat. Photon., 3(12): 696-705; Natarajan et al., 2010, Appl. Phys. Lett., 96(21): 211101; Gaggero et al., 2010, Appl. Phys. Lett., 97(15): 151108; Knill et al., 2001, Nature, 409(6816): 46-52). Most prominently, quantum key distribution implementations (Takesue et al., 2007, Nat. Photon., 1(6): 343-348; Gisin et al., 2002, Rev. Mod. Phys., 74(1): 145-195) are currently limited in rate and range by imperfect detector characteristics. Other applications which would greatly benefit from improved single-photon detection systems include the characterization of quantum emitters (Hadfield et al., 2005, Opt. Express. 13(26): 10846-10853; Correa et al., 2012, Nano Lett, 12(6): 2953-2958; Korneev et al., 2007, IEEE J. Sel. Top. Quantum Electron., 13(4): 944-951; Reithmaier et al, 2013, arxiv:1302.3807), optical time domain reflectometry (Eraerds et al., 2010, Lightwave Technol., 28(6): 952-964) as well as picosecond imaging circuit analysis (Stellari et al., 2011, IEEE J. Quantum Electron., 47(6): 841-848).
One of the most promising technologies to achieve low noise detector characteristics are nanowire superconducting single-photon detectors (SSPDs) (Gol'tsman et al., 2001, Appl. Phys. Lett., 79(6): 705-707). SSPDs are well suited for the integration with nanophotonic circuitry and offer superior performance compared to more traditional detector technologies. The detection mechanism relies on single-photon induced hotspot creation in a superconducting nanowire which is current biased close to its critical current (Natarajan et al., 2012, Supercond. Sci. Technol., 25(6): 063001). The detection process is characterized by a fast recovery time and high quantum efficiency both for visible and infrared wavelength photons (Hadfield, 2009, Nat. Photon., 3(12): 696-705; Gol'tsman et al., 2007, IEEE Trans. Appl. Supercond., 17(2): 246-251; Marsili et al., 2013, Nat. Photon., 7: 210-214). Until recently most state-of-the-art SSPDs however, were stand-alone units absorbing fiber-coupled photons using meander wires of superconducting thin film, where photons are absorbed under normal incidence. These types of devices limit their usefulness for large scale integrated photon counting applications.
Interfacing optical circuitry and high-efficiency single photon detectors with low loss is one of the key challenges of quantum photonic technologies (O'Brien, 2007, Science, 318: 1567; Natarajan et al., 2010, Appl. Phys. Lett., 96: 211101). Ideally, these components are integrated with non-classical light sources on a scalable monolithic platform (Politi et al., 2009, IEEE J. Sel. Top. Quantum Electron., 15: 1673). Integrated single photon detectors are key components for enabling functionality in nanophotonics and on-chip quantum optical technology. In particular, quantum information processing requires efficient interfacing of photonic circuitry with single photon detectors for scalable implementations (O'Brien, 2007, Science, 318(5856): 1567-1570). On the one hand, optical waveguide technology is one of the most promising routes to build complex quantum optical systems on-chip (Politi et al., 2009, IEEE J. Sel. Topics Quantum Electron., 15(6): 1673-1684; Schaeff et al., 2012, Opt. Exp., 20(15) 16145-16153). On the other hand, SSPDs are emerging as the photon-counting technology best suited for integrated quantum information technology (Hadfield, 2009, Nat. Photon., 3(12) 696-705). High timing accuracy, low noise and high sensitivity at telecom wavelengths show the potential to satisfy the demands of quantum technology (Natarajan et al., 2012, Supercond. Sci. Technol., 25(6): 063001-1-063001-16).
Most of today's SSPDs are, however, designed for stand-alone operation and typically consist of a single detector device coupled to a single mode optical fiber (Slysz et al., 2006, Appl. Phys. Lett., 88(26): 261113-1-261113-3; Korneev et al., 2007, IEEE J. Sel. Topics Quantum Electron., 13(4) 944-951). While the compatibility of quantum waveguide circuits and SSPDs has been successfully demonstrated (Natarajan et al., 2010, Appl. Phys. Lett., 96(21): 211101-1-211101-3), the coupling of photons from a chip to a separate detector limits the performance of this approach. More complex (Shadbolt et al., 2012, Nat. Photon., 6(1): 45-49) or larger scale (Peruzzo et al., 2010, Science, 329(5998): 1500-1503) nanophotonic networks thus require a complementary detector architecture—ideally embedded directly into the waveguide circuitry.
Thus, there is a need in the art for improved devices and systems for single photon detection. The present invention satisfies this unmet need.